[Users] About the thorn Einstein exact

[Ian Hinder]

On 30 Oct 2017, at 03:03, Nisa Amir <nisaamir at math.qau.edu.pk> wrote:

> Hello,
> 
> I am new to Einstein toolkit and m doing my resarch on it for M.phil dissertion. Can you please guide me how to add a metric in polar coordinates in Einstein exact thorn in Einstein toolkit and how to generate a new thorn for this metric using kranc package.
> your help will be highly appreciated.

Hi,

(resent with CC to ET list)

Apologies for the long delay in replying.  Can you give a bit of background about what you want to do?

There are two possibilities. First, you can have a numerical grid in r, th and ph.  Since the evolution equations are spatially covariant (almost; the gauge conditions are not always), you can do this, but it might not be what you really want.  Most of the Einstein Toolkit assumes that you have an x,y,z type coordinate system, so to make use of it, you probably want to express your initial data in Cartesian-type coordinates.  So, for example, if you had Kerr in Boyer-Lindquist coordinates, you would first change coordinates and basis using the usual transformation, and then evaluate the metric and extrinsic curvature on the x,y,z grid.  Is that what you want to do?

-- 
Ian Hinder
http://members.aei.mpg.de/ianhin

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